The present invention relates to radio frequency resonant tags for protection of articles of sale from theft. The tag comprises a resonant circuit containing one or more conducting patterns adjacent to or separated by one or more dielectric films without any requirement for direct connection of opposite ends of a single conducting pattern or multiple conducting patterns. Conducting patterns useful in the present invention may comprise polymer-based electronically conducting paints or inks applied via conventional printing, coating or digital printing methods to the item of sale. Alternatively, one or several of the patterns may comprise a metallic foil conductor.
Various multiple frequency tags have been described for use in detection of theft of articles on sale.
For example, Kajfez et al. (WO 95/05647) describe a multiple frequency tag comprised of a dielectric substrate. A first resonant circuit including a first inductor coil and having a first predetermined resonant frequency is located on the first surface of the substrate. A second resonant circuit including a second inductor coil and having a second predetermined resonant frequency which preferably is different from the first predetermined resonant frequency is located on the second surface of the substrate. The first inductor coil is positioned on the substrate to partially overlay the second inductor coil in a manner which minimizes the magnetic coupling between the first and second coils. The tag may be employed in any type of detection system including an electronic article security system for protecting articles of sale from theft. Tags of this kind are manufactured by lamination of aluminum foils on a dielectric substrate. This substrate is subsequently printed and etched to form the resonant coils and then coated with adhesive and a protective strippable cover. It is then cut to size and shape.
A corresponding manufacturing process for a similar resonant tag to be utilized for the same purpose has been disclosed by Imaichi et al. in EP 070318 B1.
Hult{dot over (a)}ker in U.S. Pat. No. 4,9292,928 discloses the application of ink comprising magnetizable particles to a theft protection device.
Appalucci et al., in U.S. Pat. No. 5,142,270 and U.S. Pat. No. 5,241,299, describe a stabilized resonant tag circuit and deactivator for use in an electronic article surveillance system. The tag disclosed in these patents has a substantially planar dielectric substrate having conductors placed on either side where at least one of the conductors includes an inductor. The tag is stabilized by a flexible, substantially planar, tear-resistant, polymeric film adhered to and covering one of the conductors and the substrate. The film provides a vapor barrier which minimizes the effects of body detuning on the circuit and promotes the secured integrity of the tag. The tag may further comprise a deactivator for deactivating the tag in response to an electromagnetic field of sufficient energy to destroy the resonant properties of the circuit, the deactivator being an indented portion of at least one of the conductors such that the conductors are closer to each other at the indented portion than at the remainder of the conductor. The conductors of this device are made of a metallic conductor material such as aluminum foil and prepared using an extrusion coating process not described. The polymeric film which adheres to the conductors and the substrate provide mechanical stability, while the covering polymeric film provides a thin layer impervious to water vapor or other contaminants which may alter the resonating frequency.
U.S. Pat. No. 6,031,458 describes a polymeric radio frequency resonant tag comprising a first conducting pattern connected to a first capacitor electrode applied to a substrate, a dielectric film applied to the first conducting pattern and first capacitor electrode, and a second conducting pattern connected to a second capacitor electrode applied to dielectric film. A connector links the first and second conducting patterns to form an inductive element.
Alternatively, the dielectric film is replaced at the region intended to form a contact electrode via a local capacitor with a capacitor composite applied to the first capacitor electrode and a dielectric film located adjacent to the capacitor composite and applied to the first conductive pattern.
An object of the present invention is to provide radio frequency resonant tags.
In one embodiment, the tag comprises a resonant circuit containing a single conducting pattern having a first end and a second end and a dielectric film adjacent to or surrounding the single conducting pattern. In this embodiment, a selected frequency is transmitted through the conducting pattern from the first end to the second end. The frequency is then transmitted back to the first end of the conducting pattern via the dielectric film without requiring direct connection of the first and second ends of the conducting pattern.
In another embodiment, the radio frequency resonant tag comprises a resonant circuit containing multiple conducting patterns each separated by a dielectric film. In this embodiment, the selected frequency is transmitted from one conducting pattern to another via the dielectric film without requiring direct connection of the conducting patterns.